The invention relates to a water piping arrangement, and in particular to a water piping arrangement for avoiding adverse effect to the piping system based on a thermal stratification which is formed by a cavity flow which is generated in a closed pipe branched from a main pipe
A various branch pipes are generally connected to a main water pipe in a power plant or the other types of plant, in which some branch pipes are used during only the starting operation or the maintenance of the plant and closed by a shut-off valve provided in the branch pipes after the operation of the plant is transferred to a normal operation.
The inventors of the present application have found that such a branch pipe closed by a shut-off valve (hereinafter, referred to a closed branch pipe) functions as a deep recess formed in a main pipe, and that, within the closed branch pipe, a cavity flow is induced by the water flow in the main pipe. If the cavity flow is affected by a heat dissipating action of the wall of the branched pipe, a thermal stratification appears in the water within the closed branch pipe, and the water temperature is suddenly changed across the thermal stratification so that a large thermal stress is generated in the pipe.
In the prior art, such a thermal stress in the pipes, based on the thermal stratification generated by the cavity flow, is not considered in the calculation of the piping design. If a thermal stratification appears in a pipe, in particular in an elbow joint of the piping system, a crack may be resulted in the elbow joint due to the thermal stress in the elbow joint.
The invention is directed to solve the above-described problem of the prior art, and to provide a piping arrangement of a branch pipe for avoiding adverse effect to the piping system, based on a thermal stratification generated by a cavity flow in the closed branch pipe.
According to the invention, there is provided a piping arrangement which comprises a main pipe allowing a water flow; a branch pipe connected to the main pipe; and cavity flow inhibiting means provided between the main pipe and the branch pipe.
The cavity flow inhibiting means may comprise:
a swirl preventing plate including at least two plates which intersect each other with an intersecting line extending in the direction of the flow in the branch pipe;
a sleeve which has a inner diameter larger than the outer diameter of the branch pipe and enclose a portion of the branch pipe connected to the main pipe;
a deflecting member provided over a portion of the branch pipe connected to the main pipe;
an orifice provided in the branch pipe;
a tube member which is provided in a portion of the branch pipe connected to the main pipe and has different inner diameters one of which is larger than that of the closed branch pipe;
an entrance radius enlarged portion with the sectional area of its flow channel being gradually reduced from the main pipe toward the branch pipe. cross pipe; or
an inclined connecting pipe for obliquely connecting the branch pipe to the main pipe.
According to another feature of the invention, a piping arrangement of a branch pipe connected to a main pipe for allowing water to flow therethrough is provided. The branch pipe includes a cross pipe connected perpendicularly to the main pipe and a horizontal pipe connected to the cross pipe by an elbow joint so as to horizontally extend. The piping arrangement is characterized by the elbow joint being disposed in an area nearer than a transition ozone where a cellular vortex, generated in the branch pipe, is transformed into twister vortex.
The elbow joint is preferably disposed in a range within six times of the inner diameter of the branch pipe.